Applicants herein and others have conducted extensive research intended to yield curable precursors which exhibit high-temperature stability, good structural strength and cure without the production of gaseous by-products to produce void-free resin composites and molding compounds. It has long been known that polyimides exhibit certain desirable high temperature characteristics and good structural strength. However, these prior art materials where generally cured by condensation reactions and therefore resulted in cured products which contained voids. As a result of the prior work of Applicants herein, it was discovered that the reaction product of conventional dianhydrides with aminophenylacetylenes, with or without diamines, produced acetylene-terminated polyimide precursors which exhibited desirable characteristics insofar as these materials yielded essentially void-free products when cured. However, these precursors exhibit relatively high melting points and as such are difficult to process.
Other attempts to make processable polyimide or diimide precursors have resulted in similar results in that the products made from propargyl terminated polyimides or diimides are high melting and are generally intractable. See, for example, U.S. Pat. Nos. 3,897,395 and 3,998,786 issued to Gaetano Francis D'Alelio. The D'Alelio Patents disclose polyimides derived from a vast shopping list of reactants. However, an examination of the D'Alelio disclosures will reveal that the products prepared exhibit very high melting points and are generally insoluble in conventional solvents.
In the closest known prior art, acetylene substituted diimides have been made from the dianhydrides benzophenonetetracarboxylic dianhydride and pyromellitic dianhydride. Typical acetylenic diimides of this type are shown below: ##STR1## These prior art compounds melt at temperatures in excess of 200.degree. C.
Prior art acetylene substituted-polyimide oligomers which are derived from three components generally melt at temperatures in the order of 196.degree. C. to 200.degree. C. and are represented by the following general structure: ##STR2## where Ar is derived from conventional dianhydrides and R is derived from a polyaryl diamine.
These prior art diimide and polyimide precursors are limited in their usefulness because of their high melting points and general insolubilities in conventional solvents. Therefore, Applicants herein and others, have conducted studies that are designed to obtain diimide and polyimide precursors having low melting points and high solubilities in conventional solvents. Low melting points and increased solubilities in conventional low boiling solvents are sought to facilitate the processing of these materials are resins for composites, molding compounds and/or adhesives.